This invention relates to carburetors for internal combustion engines, and more particularly to apparatus for controllably opening the choke valve of a carburetor.
Most carburetors have a choke valve at the inlet of the air passage through the carburetor. This choke valve is initially closed if the engine is cold when started. At start up, the choke valve is moved to a first open or "choke break" position and then gradually moved to a fully open position as the engine heats up. To accomplish this, the choke valve is controlled by both a vacuum motor of some type and a bimetalic coil. The vacuum motor is used to provide the initial choke opening or "choke break" when the engine first starts. From then on, the heat generated by the engine as it warms up is supplied to the bimetalic coil. This coil exerts a closing force on the choke valve which gradually lessens as the engine warms. This allows the choke valve to slowly open as the engine heats up until the choke valve is fully opened. Once the choke valve is fully opened, it remains open during the remainder of engine operation.
It is known that the majority of engine emissions occur during the choke opening cycle because the engine is usually provided a richer fuel mixture at this time. Further, there is a recent Federal requirement that the choke break mechanism of the carburetor be tamperproofed, so once the carburetor has been qualified during manufacturing, the choke settings cannot be thereafter adjusted. Thus the emissions generated by the engine during its initial warm-up period can be controlled.
One problem with conventional choke opening mechanisms is the need to improve both cold starting and engine driveability while keeping engine emissions down during the choke cycle. This problem can be solved by providing some type of programmed control of the choke valve so its opening is more closely regulated than is currently the case using present mechanical systems. Such an electronic control strategy would have both improved cold-starting characteristics as well as improved engine driveability during the choke operating cycle.